In late August, I dug out a bed down two feet, filled 1/2 full with horse manure, then 4 inches of sand, then filled to surface level with composted top soil. I then constructed a cold frame over the top and seeded.

The manure is decomposing and warming the soil, and with the protection and help of the cold frame, I'm getting temps up to 70 degrees F inside, even when it's freezing out. Neat, huh?

My mom grows her garden in about 80 percent (seasoned) horse manure.When i say seasoned i mean just old enough that it doesn't burn the plants.But still hot enough to steam like crazy on cool mornings.However she hasn't tried covering it and growing earlier or later than normal.
Noticed yesterday morning while the chickens where scratching in my mulch pile the stem was just rolling.I got pretty much the same idea that you used.But didn't no it would work in winter.I was just going to try it in early spring,to start stuff out earlier this year. Hum a winter garden.Cool! Id love a good fresh vine ripened tomato most of all.

The guy that wrote "Four Season Gardening" lives in Vermont or NH, doesn't he? He uses cold frames and plastic covered hoops and greenhouses and has salad every night, even when snow is thick on the ground. I enjoyed the book and don't even need its tips where I live. Go for it and get out the salad dressing!

The guy that wrote "Four Season Gardening" lives in Vermont or NH, doesn't he? He uses cold frames and plastic covered hoops and greenhouses and has salad every night, even when snow is thick on the ground. I enjoyed the book and don't even need its tips where I live. Go for it and get out the salad dressing!

I think that in the French Intensive method they pile fresh manure around the outside of the cold frame, eliminating the need to dig so deep. As it decomposes it both warms and fertilizes. Greens grow quite well in the 50's and tolerate light frost; I grow them here without covering them. Beets too. With temps in the 70's you could grow lots of stuff, although you might need a grow light to lengthen the days.